Internal Combustion Engine Piston

ABSTRACT

An internal combustion engine piston includes a piston crown, a thrust-side skirt, an anti-thrust-side skirt, a first apron, and a second apron. The first and second aprons are connected to the thrust-side and anti-thrust-side skirts through connecting sections. Each connecting section has a thickness that gradually increases as followed from a proximal longitudinal end to a distal longitudinal end, wherein the proximal longitudinal end is closer to the piston crown, and the distal longitudinal end is closer to a distal longitudinal end of a corresponding one of the thrust-side and anti-thrust-side skirts.

BACKGROUND OF THE INVENTION

The present invention relates to internal combustion engine pistonswhich may be adapted to motor vehicles.

In an internal combustion engine, a piston is subject to high combustionpressure, and thereby subject to a side force because of inclination ofa connecting rod with respect to the piston. The side force presses thepiston on a cylinder wall, and causes a large frictional force between athrust-side skirt of the piston and the cylinder wall. Accordingly,internal combustion engine pistons are designed to bear such sideforces, and reduce such frictional forces. On the other hand, there isdemand for weight reduction of internal combustion engine pistons.

Japanese Patent Application Publication No. 2008-190357 discloses aninternal combustion engine piston which includes a thrust-side skirt, ananti-thrust-side skirt, and a pair of aprons between the thrust-sideskirt and the anti-thrust-side skirt, where each connecting sectionbetween one of the skirts and one of the aprons is formed with a stressdispersing portion for dispersing a stress that is concentrated in theconnecting section due to difference in thermal expansion and elasticdeformation between the skirt and the apron.

SUMMARY OF THE INVENTION

In the internal combustion engine piston according to Japanese PatentApplication Publication No. 2008-190357, each stress dispersing portionis implemented by a projection which extends outwardly from a lower endportion of the corresponding skirt. This can enhance the rigidity of thelower end portion of the skirt locally, and thereby cause the rigidityof the entire skirt to be uneven. The contact pressure between eachskirt and the cylinder wall can be locally high due to the unevenrigidity, so that the piston can be subject to a large frictional force.

In view of the foregoing, it is desirable to provide an internalcombustion engine piston which is capable of solving the problemdescribed above.

According to one aspect of the present invention, an internal combustionengine piston comprises: a piston crown defining a combustion chamber; athrust-side skirt formed integrally with the piston crown, and adaptedto be in sliding contact with a cylinder wall, the thrust-side skirthaving an arc-shaped cross-section; an anti-thrust-side skirt formedintegrally with the piston crown, and adapted to be in sliding contactwith the cylinder wall, the anti-thrust-side skirt having an arc-shapedcross-section; a first apron formed with a first piston pin boss; asecond apron formed with a second piston pin boss; a first connectingsection connecting the first apron to a first circumferential end of thethrust-side skirt; a second connecting section connecting the secondapron to a second circumferential end of the thrust-side skirt; a thirdconnecting section connecting the first apron to a first circumferentialend of the anti-thrust-side skirt; and a fourth connecting sectionconnecting the second apron to a second circumferential end of theanti-thrust-side skirt, wherein each of the first, second, third andfourth connecting sections has a thickness that gradually increases asfollowed from a proximal longitudinal end to a distal longitudinal end,wherein the proximal longitudinal end is closer to the piston crown, andthe distal longitudinal end is closer to a distal longitudinal end of acorresponding one of the thrust-side and anti-thrust-side skirts. Theinternal combustion engine piston may be configured so that: each of thefirst, second, third and fourth connecting sections has an arc-shapedcross-section whose radius of curvature gradually increases as followedfrom the proximal longitudinal end to the distal longitudinal end in apiston longitudinal direction; and an inside surface of each of thefirst, second, third and fourth connecting sections has a larger radiusof curvature than an outside surface of the each of the first, second,third and fourth connecting sections at the distal longitudinal end. Theinternal combustion engine piston may be configured so that: each of thefirst and second aprons has a curved cross-section; and each of thefirst and second connecting sections or each of the third and fourthconnecting sections includes a projection located at the distallongitudinal end, wherein the projection extends inwardly substantiallyin a piston radial direction. The internal combustion engine piston maybe configured so that: each of the first and second aprons has a curvedcross-section; and each of the first and second connecting sectionsincludes a projection located at the distal longitudinal end, whereinthe projection extends inwardly substantially in a piston radialdirection. The internal combustion engine piston may be configured sothat: each of the first and second aprons has a curved cross-section;and each of the first, second, third and fourth connecting sectionsincludes a projection located at the distal longitudinal end, whereinthe projection extends inwardly substantially in a piston radialdirection.

According to another aspect of the present invention, an internalcombustion engine piston comprises: a piston crown defining a combustionchamber; a thrust-side skirt formed integrally with the piston crown,and adapted to be in sliding contact with a cylinder wall, thethrust-side skirt having an arc-shaped cross-section; ananti-thrust-side skirt formed integrally with the piston crown, andadapted to be in sliding contact with the cylinder wall, theanti-thrust-side skirt having an arc-shaped cross-section; a first apronformed with a first piston pin boss; a second apron formed with a secondpiston pin boss; a first connecting section connecting the first apronto a first circumferential end of the thrust-side skirt; a secondconnecting section connecting the second apron to a secondcircumferential end of the thrust-side skirt; a third connecting sectionconnecting the first apron to a first circumferential end of theanti-thrust-side skirt; and a fourth connecting section connecting thesecond apron to a second circumferential end of the anti-thrust-sideskirt, wherein at least one of the thrust-side and anti-thrust-insideskirts is formed so that rigidity of the at least one of the thrust-sideand anti-thrust-side skirts is substantially uniform from a proximallongitudinal end to a distal longitudinal end, wherein the proximallongitudinal end is closer to the piston crown than the distallongitudinal end.

According to a further aspect of the present invention, an internalcombustion engine piston comprises: a piston crown defining a combustionchamber; a thrust-side skirt formed integrally with the piston crown,and adapted to be in sliding contact with a cylinder wall, thethrust-side skirt having an arc-shaped cross-section; ananti-thrust-side skirt formed integrally with the piston crown, andadapted to be in sliding contact with the cylinder wall, theanti-thrust-side skirt having an arc-shaped cross-section; a first apronformed with a first piston pin boss; a second apron formed with a secondpiston pin boss; a first connecting section connecting the first apronto a first circumferential end of the thrust-side skirt; a secondconnecting section connecting the second apron to a secondcircumferential end of the thrust-side skirt; a third connecting sectionconnecting the first apron to a first circumferential end of theanti-thrust-side skirt; and a fourth connecting section connecting thesecond apron to a second circumferential end of the anti-thrust-sideskirt, wherein at least one of the thrust-side and anti-thrust-sideskirts is formed so that deformation of the at least one of thethrust-side and anti-thrust-side skirts is substantially uniform from aproximal longitudinal to a distal longitudinal end in a pistonlongitudinal direction while the at least one of the thrust-side andanti-thrust-side skirts is sliding in contact with the cylinder wallduring piston stroke, wherein the proximal longitudinal end is closer tothe piston crown than the distal longitudinal end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an internal combustion engine pistonaccording to a first embodiment of the present invention from its bottomside. FIG. 1B is an enlarged partial side-sectional view of the internalcombustion engine piston taken along the line A-A in FIG. 1A.

FIG. 2 is a side view of the internal combustion engine piston accordingto the first embodiment.

FIG. 3 is a partially cutaway front view of the internal combustionengine piston according to the first embodiment.

FIG. 4 is a bottom view of the internal combustion engine pistonaccording to the first embodiment.

FIG. 5 is a perspective view of the internal combustion engine pistonaccording to the first embodiment, where skirts and aprons are shown inthe form of separated sections, and outside surfaces of connectingsections are indicated by hatching pattern.

FIG. 6 is a partially cutaway perspective view of the internalcombustion engine piston according to the first embodiment, where theskirts and aprons are shown in the form of separated sections, andinside surfaces of connecting sections are indicated by hatchingpattern.

FIG. 7 is a side sectional view of the internal combustion engine pistonin sliding contact with a cylinder wall in a cylinder block.

FIG. 8 is a graphic diagram showing the amount of deformation of athrust-side skirt with respect to a position in the thrust-side skirt ina case of the internal combustion engine piston according to the firstembodiment and in a case of an internal combustion engine pistonaccording to a reference example.

FIG. 9 is a graphic diagram showing a frictional force with respect to acrank angle in a case of the internal combustion engine piston accordingto the first embodiment and in a case of the internal combustion enginepiston according to the reference example.

FIG. 10 is a perspective view of an internal combustion engine pistonaccording to a second embodiment of the present invention from itsbottom side.

FIG. 11 is a bottom view of the internal combustion engine pistonaccording to the second embodiment.

FIG. 12 is a perspective view of an internal combustion engine pistonaccording to a third embodiment of the present invention from its bottomside.

FIG. 13 is a bottom view of the internal combustion engine pistonaccording to the third embodiment.

FIG. 14 is a perspective view of the internal combustion engine pistonaccording to the third embodiment, where skirts and aprons are shown inthe form of separated sections, and outside surfaces of connectingsections are indicated by hatching pattern.

DETAILED DESCRIPTION OF THE INVENTION

Internal combustion engine pistons according to first to thirdembodiments of the present invention are adapted to four-cycle gasolineengines.

<First Embodiment> As shown in FIG. 7, a piston 1 is provided in acylindrical bore formed in a cylinder block 2, so that piston 1 is insliding contact with a cylinder wall 3 of the bore. Piston 1, cylinderwall 3, and cylinder head not shown define a combustion chamber 4.Piston 1 is linked to a crankshaft not shown through a piston pin 5 anda connecting rod 6.

Piston 1 is formed integrally from an Al—Si aluminum alloy, AC8A, bycasting. As shown in FIGS. 1A to 4, piston 1 has a cylindrical shape,which is formed with a piston crown 7 defining the combustion chamber 4on a crown top 7 a; a thrust-side skirt 8 formed integrally with aperiphery of a lower end portion of piston crown 7, and adapted to be insliding contact with cylinder wall 3, wherein thrust-side skirt 8 has anarc-shaped cross-section as viewed in the longitudinal direction ofpiston 1; an anti-thrust-side skirt 9 formed integrally with theperiphery of the lower end portion of piston crown 7, and adapted to bein sliding contact with cylinder wall 3, wherein anti-thrust-side skirt9 has an arc-shaped cross-section as viewed in the longitudinaldirection of piston 1; a first apron 11 formed with a first piston pinboss 13; a second apron 12 formed with a second piston pin boss 14; afirst connecting section 10 connecting the first apron 11 to a firstcircumferential end of thrust-side skirt 8; a second connecting section10 connecting the second apron 12 to a second circumferential end ofthrust-side skirt 8; a third connecting section 10 connecting the firstapron 11 to a first circumferential end of anti-thrust-side skirt 9; anda fourth connecting section 10 connecting the second apron 12 to asecond circumferential end of anti-thrust-side skirt 9.

Piston crown 7 is in the form of a relatively thick disc. Piston crown 7is formed with valve recesses not shown in crown top 7 a for preventinginterference with intake and exhaust valves, and also with ring grooves7 b, 7 c and 7 d in the periphery for retaining three piston rings suchas a pressure ring and an oil ring.

Thrust-side and anti-thrust-side skirts 8 and 9 are arrangedsymmetrically with respect to a plane passing through a centrallongitudinal axis of piston 1. Each of thrust-side and anti-thrust-sideskirts 8 and 9 has an arc-shaped cross-section whose thickness isrelatively thin substantially entirely. When piston 1 is travelingtoward a bottom dead center position, for example, on expansion stroke,thrust-side skirt 8 is pressed on cylinder wall 3 with an inclinationresulting from a relationship in angle between piston 1 and connectingrod 6. On the other hand, when piston 1 is traveling toward a top deadcenter position, for example, on compression stroke, anti-thrust-sideskirt 9 is pressed on cylinder wall 3 with an opposite inclinationresulting from the relationship in angle between piston 1 and connectingrod 6. In general, the force pressing the thrust-side skirt 8 oncylinder wall 3 is larger than the force pressing the anti-thrust-sideskirt 9 on cylinder wall 3, because thrust-side skirt 8 is subject tocombustion pressure.

Each of thrust-side and anti-thrust-side skirts 8 and 9 has atrapezoidal side section with inclined edges as viewed from the frontside of thrust-side or anti-thrust-side skirt 8 or 9, as shown in FIG.2. Namely, the width of each of thrust-side and anti-thrust-side skirts8 and 9 increases as followed from an upper end portion 8 a or 9 a to alower end portion 8 b or 9 b. Each of thrust-side and anti-thrust-sideskirts 8 and 9 is formed with a substantially flat lower end edge 8 c or9 c.

Each apron 11 or 12 has an upper end formed integrally with the lowerend of piston crown 7, and has a curved cross-section that is slightlycurved outwardly as viewed in the longitudinal direction of piston 1.The radius of curvature of the cross-section of apron 11 or 12 is setlarger than that of thrust-side or anti-thrust-side skirt 8 or 9, forexample, set to about from 150-300 mm. As shown in FIG. 2, aprons 11 and12 are formed to extend with inclination with respect to thelongitudinal axis of piston 1, so that aprons 11 and 12 spread asfollowed from the upper end to the lower end. The thickness of thecross-section of each apron 11 or 12 is relatively large. Each apron 11or 12 is formed with piston pin boss 13 or 14 substantially at thecenter in the circumferential direction of piston 1. Each piston pinboss 13 or 14 includes a piston pin hole 13 a or 14 a which supports oneof the longitudinal ends of piston pin 5.

Each connecting section 10 has an arc-shaped cross-section as viewed inthe longitudinal direction of piston 1, extending between apron 11 or 12and thrust-side or anti-thrust-side skirt 8 or 9 in the circumferentialdirection of piston 1. As indicated by hatching pattern in FIGS. 1A and6, an inside surface 16 of connecting section 10 has a radius ofcurvature that gradually and continuously increases as followed from anupper end portion 16 a to a lower end portion 16 b in the longitudinaldirection of piston 1. Similarly, as indicated by hatching pattern inFIGS. 1A and 5, an outside surface 17 of connecting section 10 has aradius of curvature that gradually and continuously increases asfollowed from an upper end portion 17 a to a lower end portion 17 b inthe longitudinal direction of piston 1. Specifically, the radius ofcurvature of each of inside and outside surfaces 16 and 17 is set toincrease continuously and linearly from about 10 mm to about 30 mm asfollowed from upper end portion 16 a or 17 a to lower end portion 16 bor 17 b in the longitudinal direction of piston 1.

The arc width W of inside surface 16 and the arc width W1 of outsidesurface 17 change as followed in the piston longitudinal direction,where the rate of change of the arc width W is different from that ofthe arc width W1. Specifically, the arc width W of outside surface 17 isset relatively small, and the rate of change from upper end portion 17 ato lower end portion 17 b is set relatively small. On the other hand,the arc width W1 of inside surface 16 is set relatively large, and therate of change from upper end portion 16 a to lower end portion 16 b isset relatively large as compared to outside surface 17. Accordingly, thethickness of connecting section 10 gradually increases as followed froma proximal longitudinal end to a distal longitudinal end, where theproximal longitudinal end is closer to piston crown 7, and the distallongitudinal end is closer to a distal longitudinal end (lower end edge8 c or 9 c) of a corresponding one of thrust-side and anti-thrust-sideskirts 8 and 9. The substantially flat shape of inside surface 16 ofconnecting section 10 is effective for setting the rigidity ofthrust-side and anti-thrust-side skirts 8 and 9 to be substantiallyuniform entirely, i.e. both in the circumferential direction and in thepiston longitudinal direction.

The shapes of thrust-side and anti-thrust-side skirts 8 and 9,connecting sections 10, and aprons 11 and 12 constitute a truncated coneshape with an elliptic cross-section as viewed from the bottom side, asshown in FIGS. 1A, 2 and 4.

The inside surface 16 of each connecting section 10 is formed with aprojection 18 locally at lower end portion 16 b. As shown in FIG. 1B,each projection 18 is formed integrally with the lower end portion 16 bof inside surface 16 of connecting section 10, where projection 18 hasan arc-shaped inside surface, and a lower edge which is the thickest andflush with the lower edge of inside surface 16. The thickness ofprojection 18 is set to decrease as followed upwardly from lower endedge 18 b. An upper end edge 18 a of projection 18 is smoothly andcontinuously connected to lower end portion 16 b of inside surface 16.

The provision of projection 18 is effective for enhancing the rigidityof the lower edge of thrust-side or anti-thrust-side skirt 8 or 9 thatis a free end, and thereby setting the rigidity of thrust-side oranti-thrust-side skirt 8 or 9 more uniform.

With the arc-shaped cross-section, each connecting section 10 functionsas a spring to suppress deformation of thrust-side or anti-thrust-sideskirt 8 or 9, when thrust-side or anti-thrust-side skirt 8 or 9 ispressed on cylinder wall 3 during reciprocating motion of piston 1.Moreover, aprons 11 and 12, which have curved cross-sections, alsofunction as springs, although the effect of aprons 11 and 12 is smallerthan that of connecting sections 10. In this way, connecting sections10, and aprons 11 and 12 serve to increase the contact area betweenthrust-side or anti-thrust-side skirt 8 or 9 and cylinder wall 3, andthereby prevent the contact pressure therebetween from locallyincreasing. In other words, thrust-side and anti-thrust-side skirts 8and 9, connecting sections 10, and aprons 11 and 12 form a substantiallyelliptic cross-section as viewed in the longitudinal direction of piston1, where connecting sections 10 and aprons 11 and 12 function as aspring so as to absorb or disperse or suppress the contact pressureapplied to thrust-side or anti-thrust-side skirt 8 or 9.

The feature that the radius of curvature of connecting section 10gradually increases as followed from upper end portions 16 a and 17 a tolower end portions 16 b and 17 b, is effective for setting the rigidityof thrust-side or anti-thrust-side skirt 8 or 9 at the circumferentialends connected to apron 11 or 12 to be uniform in the pistonlongitudinal direction. If the thickness of connecting section 10 isuniform between upper end portion 16 a or 17 a and lower end portion 16b or 17 b, the rigidity gradually decreases from upper end portion 16 aor 17 a and lower end portion 16 b or 17 b, because the lower endportion 16 b or 17 b is a free end. This decrease is cancelled by theforegoing feature. In this way, the feature is effective for providinguniform contact between thrust-side or anti-thrust-side skirt 8 or 9 andcylinder wall 3, and thereby reducing the contact pressure and thefriction therebetween.

The provision of projection 18 is effective for further enhancing therigidity of the lower end portion of thrust-side or anti-thrust-sideskirt 8 or 9. Since the lower end portion 8 b or 9 b of thrust-side oranti-thrust-side skirt 8 or 9 is a free end, the rigidity of the lowerend portion 8 b or 9 b tends to be relatively low. However, projection18 serves to further enhance the rigidity of lower end portion 9 b inaddition to the effective shape of connecting section 10, and therebyset the rigidity of thrust-side or anti-thrust-side skirt 8 or 9uniform. This is effective for providing uniform contact betweenthrust-side or anti-thrust-side skirt 8 or 9 and cylinder wall 3, mainlyin the piston longitudinal direction, and thereby reducing the contactpressure and the friction therebetween.

FIG. 8 shows a result of an experiment in which the amount ofdeformation of a thrust-side skirt at a point between the upper end andthe lower end is measured under the same condition that the thrust-sideskirt is in contact with cylinder wall 3 on expansion stroke, in a caseof piston 1 according to the first embodiment which is indicated by asolid line, and in a case of a piston according to a reference examplewhich is indicated by a broken line. In the piston according to thereference example, the amount of deformation significantly increases asthe position moves from the upper end to the lower end. In contrast, inpiston 1 according to the present embodiment, the amount of deformationis smaller and more uniform all over the range between the upper end andthe lower end, although it is slightly relatively large at a positionslightly below the upper end, and at or near the lower end. This isachieved because the characteristic shape of connecting section 10, andthe provision of projection 18 serve to set the rigidity of thrust-sideskirt 8 substantially uniform entirely. In this way, thrust-side oranti-thrust-side skirt 8 or 9 is formed so that deformation ofthrust-side or anti-thrust-side skirt 8 or 9 is substantially uniformfrom a proximal longitudinal to a distal longitudinal end in a pistonlongitudinal direction while thrust-side or anti-thrust-side skirt 8 or9 is sliding in contact with cylinder wall 3 during piston stroke,wherein the proximal longitudinal end is closer to piston crown 7 thanthe distal longitudinal end.

FIG. 9 shows a history of a frictional force applied to a piston whichis calculated by numerical analysis in the case of piston 1 according tothe present embodiment, and in the case of the piston according to thereference example. The horizontal axis represents the crank angle,whereas the vertical axis represents the frictional force. As shown inFIG. 9, the frictional force in the present embodiment indicated by asolid line is smaller than in the reference example indicated by abroken line, specifically in the range of about 0 to 90 degrees. This isachieved by the characteristic structure of piston 1.

<Second Embodiment> FIGS. 10 and 11 show a second embodiment in whichthrust-side and anti-thrust-side skirts 8 and 9 are formed and arrangedasymmetrically with respect to the plane passing through the centrallongitudinal axis of piston 1. Specifically, the circumferential lengthX of anti-thrust-side skirt 9 is set shorter than the circumferentiallength X1 of thrust-side skirt 8. Namely, the contact area ofanti-thrust-side skirt 9 with cylinder wall 3 is set smaller than thatof thrust-side skirt 8. This is because the pressing force applied toanti-thrust-side skirt 9 is smaller than the pressing force applied tothrust-side skirt 8.

The radius of curvature of each of two connecting sections 10 closer tothrust-side skirt 8 is set equal to that in the first embodiment. On theother hand, the radius of curvature of each of two connecting sections10 a closer to anti-thrust-side skirt 9 is set smaller than that ofconnecting sections 10 closer to thrust-side skirt 8.

Moreover, the thickness, and circumferential length of each ofprojections 18B closer to anti-thrust-side skirt 9 are set smaller thanthose of projections 18A closer to thrust-side skirt 8 or than those inthe first embodiment.

On the other hand, the curved shapes of aprons 11 and 12 are the same asin the first embodiment.

The second embodiment is effective for reducing the total weight ofpiston 1 because of compactness of parts closer to anti-thrust-sideskirt 9, while producing the same advantageous effects as in the firstembodiment.

<Third Embodiment> FIGS. 12 to 14 show a third embodiment created basedon the first and second embodiments, in which each apron 11 or 12 iscurved slightly outwardly as viewed in FIG. 13, extending in parallel tothe longitudinal axis of piston 1 with no inclination. Namely, aprons 11and 12 are arranged in parallel to each other, in contrast to the apronsaccording to the first embodiment which constitute a truncated coneshape with a trapezoidal side-section.

The radius of curvature of outside surface 17 of connecting section 10is substantially constant all over the range from the upper end to thelower end. In contrast, the radius of curvature of inside surface 16 ofconnecting section 10 is set to increase gradually as followed fromupper end portion 16 a to lower end portion 16 b.

In this embodiment, the curved shapes of aprons 11 and 12 serve assprings, as in the first embodiment. Moreover, in connecting section 10,the feature that the radius of curvature of outside surface 17 issubstantially constant from the upper end to the lower end, and theradius of curvature of inside surface 16 increases significantly fromthe upper end to the lower end, serves to set the thickness of the lowerend portion of connecting section 10 larger enough than that of theupper end portion, and thereby set the rigidity of thrust-side oranti-thrust-side skirt 8 or 9 substantially uniform.

The shapes and spring functions of aprons 11 and 12, and connectingsections 10 serve to suppress unevenness of the rigidity of thrust-sideand anti-thrust-side skirts 8 and 9, and thereby suppress unevenness ofthe contact pressure between cylinder wall 3 and thrust-side oranti-thrust-side skirt 8 or 9.

Each apron 11 or 12 is not limited to a curved cross-section, but mayhave a substantially flat cross-section as viewed in the longitudinaldirection of piston 1. In such a case, when thrust-side oranti-thrust-side skirt 8 or 9 is pressed on cylinder wall 3, connectingsection 10 mainly serves as a spring, while aprons 11 and 12 do notserve as springs very well.

The present invention is not limited to the first to third embodiments,and may be embodied so that only thrust-side skirt 8 is provided withconnecting sections 10 and anti-thrust-side skirt 9 is provided with noconnecting sections 10, where thrust-side skirt 8 is generally subjectto high contact load.

Connecting section 10 is not limited to an arc-shaped cross-section asviewed in the longitudinal direction of piston 1, and may have a curvedcross-section formed by chamfering.

The outside surfaces of thrust-side and anti-thrust-side skirts 8 and 9may be coated with a low-friction material, in order to reduce thefriction between cylinder wall 3 and thrust-side or anti-thrust-sideskirt 8 or 9.

The material of piston 1 is not limited to aluminum alloys, but may beformed of one of various materials such as iron and magnesium.

The piston may be adapted to various internal combustion engines such assingle-cylinder types, and multiple-cylinder types, such as V-types, andW-types.

The entire contents of Japanese Patent Application 2009-058839 filedMar. 12, 2009 are incorporated herein by reference.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

1. An internal combustion engine piston comprising: a piston crown defining a combustion chamber; a thrust-side skirt formed integrally with the piston crown, and adapted to be in sliding contact with a cylinder wall, the thrust-side skirt having an arc-shaped cross-section; an anti-thrust-side skirt formed integrally with the piston crown, and adapted to be in sliding contact with the cylinder wall, the anti-thrust-side skirt having an arc-shaped cross-section; a first apron formed with a first piston pin boss; a second apron formed with a second piston pin boss; a first connecting section connecting the first apron to a first circumferential end of the thrust-side skirt; a second connecting section connecting the second apron to a second circumferential end of the thrust-side skirt; a third connecting section connecting the first apron to a first circumferential end of the anti-thrust-side skirt; and a fourth connecting section connecting the second apron to a second circumferential end of the anti-thrust-side skirt, wherein each of the first, second, third and fourth connecting sections has a thickness that gradually increases as followed from a proximal longitudinal end to a distal longitudinal end, wherein the proximal longitudinal end is closer to the piston crown, and the distal longitudinal end is closer to a distal longitudinal end of a corresponding one of the thrust-side and anti-thrust-side skirts.
 2. The internal combustion engine piston as claimed in claim 1, wherein: each of the first, second, third and fourth connecting sections has an arc-shaped cross-section whose radius of curvature gradually increases as followed from the proximal longitudinal end to the distal longitudinal end in a piston longitudinal direction; and an inside surface of each of the first, second, third and fourth connecting sections has a larger radius of curvature than an outside surface of the each of the first, second, third and fourth connecting sections at the distal longitudinal end.
 3. The internal combustion engine piston as claimed in claim 1, wherein: each of the first and second aprons has a curved cross-section; and each of the first and second connecting sections or each of the third and fourth connecting sections includes a projection located at the distal longitudinal end, wherein the projection extends inwardly substantially in a piston radial direction.
 4. The internal combustion engine piston as claimed in claim 1, wherein: each of the first and second aprons has a curved cross-section; and each of the first and second connecting sections includes a projection located at the distal longitudinal end, wherein the projection extends inwardly substantially in a piston radial direction.
 5. The internal combustion engine piston as claimed in claim 1, wherein: each of the first and second aprons has a curved cross-section; and each of the first, second, third and fourth connecting sections includes a projection located at the distal longitudinal end, wherein the projection extends inwardly substantially in a piston radial direction.
 6. An internal combustion engine piston comprising: a piston crown defining a combustion chamber; a thrust-side skirt formed integrally with the piston crown, and adapted to be in sliding contact with a cylinder wall, the thrust-side skirt having an arc-shaped cross-section; an anti-thrust-side skirt formed integrally with the piston crown, and adapted to be in sliding contact with the cylinder wall, the anti-thrust-side skirt having an arc-shaped cross-section; a first apron formed with a first piston pin boss; a second apron formed with a second piston pin boss; a first connecting section connecting the first apron to a first circumferential end of the thrust-side skirt; a second connecting section connecting the second apron to a second circumferential end of the thrust-side skirt; a third connecting section connecting the first apron to a first circumferential end of the anti-thrust-side skirt; and a fourth connecting section connecting the second apron to a second circumferential end of the anti-thrust-side skirt, wherein at least one of the thrust-side and anti-thrust-side skirts is formed so that rigidity of the at least one of the thrust-side and anti-thrust-side skirts is substantially uniform from a proximal longitudinal end to a distal longitudinal end, wherein the proximal longitudinal end is closer to the piston crown than the distal longitudinal end.
 7. An internal combustion engine piston comprising: a piston crown defining a combustion chamber; a thrust-side skirt formed integrally with the piston crown, and adapted to be in sliding contact with a cylinder wall, the thrust-side skirt having an arc-shaped cross-section; an anti-thrust-side skirt formed integrally with the piston crown, and adapted to be in sliding contact with the cylinder wall, the anti-thrust-side skirt having an arc-shaped cross-section; a first apron formed with a first piston pin boss; a second apron formed with a second piston pin boss; a first connecting section connecting the first apron to a first circumferential end of the thrust-side skirt; a second connecting section connecting the second apron to a second circumferential end of the thrust-side skirt; a third connecting section connecting the first apron to a first circumferential end of the anti-thrust-side skirt; and a fourth connecting section connecting the second apron to a second circumferential end of the anti-thrust-side skirt, wherein at least one of the thrust-side and anti-thrust-side skirts is formed so that deformation of the at least one of the thrust-side and anti-thrust-side skirts is substantially uniform from a proximal longitudinal to a distal longitudinal end in a piston longitudinal direction while the at least one of the thrust-side and anti-thrust-side skirts is sliding in contact with the cylinder wall during piston stroke, wherein the proximal longitudinal end is closer to the piston crown than the distal longitudinal end. 